It happened two days after a system update, however, I noticed nothing particularly interesting in standard out during the update and I had no problems until tonight. While running VirtualBox and installing a windows xp host, the system seemingly aribitrarily crashed, closed X, and spit out the above error for the first time when I attempted to login.

While attempting to recover from this problem I noticed a passwd.pacnew, and shadow.pacnew among others which did not seem pertinent. I made no changes to passwd or shadow. I made no changes to /etc/pam.d/* or anything related to PAM.

I formerly used slim, configured to automatically login the only non-root user without a password, but disabled most daemons to try to solve the problem.

Does anyone have any suggestions to alleviate or diagnose this problem? I really don't want to reinstall fresh and even lose the programs I have to reinstall.

Nothing is too wonderful to be true, if it be consistent with the laws of nature -- Michael FaradayYou assume people are rational and influenced by evidence. You must not work with the public much. -- Trilby----How to Ask Questions the Smart Way

Sorry I suppose my wording was unclear. I think /etc/passwd and /etc/shadow are both potentially relevant files, but from googling about this pacnew most others have dealt with this pacnew by ignoring it since it is based off of system defaults rather than the actual users in the system (and many have had problems from incorrectly mergeing these two pacnew files). I meant the other .pacnew files seemed irrelevant but I get:

I did the changes to /etc/mkinitcpio.conf, but just in case here it is currently:

# vim:set ft=sh
# MODULES
# The following modules are loaded before any boot hooks are
# run. Advanced users may wish to specify all system modules
# in this array. For instance:
# MODULES="piix ide_disk reiserfs"
MODULES=""
# BINARIES
# This setting includes any additional binaries a given user may
# wish into the CPIO image. This is run last, so it may be used to
# override the actual binaries included by a given hook
# BINARIES are dependency parsed, so you may safely ignore libraries
BINARIES=""
# FILES
# This setting is similar to BINARIES above, however, files are added
# as-is and are not parsed in any way. This is useful for config files.
FILES=""
# HOOKS
# This is the most important setting in this file. The HOOKS control the
# modules and scripts added to the image, and what happens at boot time.
# Order is important, and it is recommended that you do not change the
# order in which HOOKS are added. Run 'mkinitcpio -H <hook name>' for
# help on a given hook.
# 'base' is _required_ unless you know precisely what you are doing.
# 'udev' is _required_ in order to automatically load modules
# 'filesystems' is _required_ unless you specify your fs modules in MODULES
# Examples:
## This setup specifies all modules in the MODULES setting above.
## No raid, lvm2, or encrypted root is needed.
# HOOKS="base"
#
## This setup will autodetect all modules for your system and should
## work as a sane default
# HOOKS="base udev autodetect block filesystems"
#
## This setup will generate a 'full' image which supports most systems.
## No autodetection is done.
# HOOKS="base udev block filesystems"
#
## This setup assembles a pata mdadm array with an encrypted root FS.
## Note: See 'mkinitcpio -H mdadm' for more information on raid devices.
# HOOKS="base udev block mdadm encrypt filesystems"
#
## This setup loads an lvm2 volume group on a usb device.
# HOOKS="base udev block lvm2 filesystems"
#
## NOTE: If you have /usr on a separate partition, you MUST include the
# usr, fsck and shutdown hooks.
HOOKS="base udev autodetect modconf block filesystems usbinput fsck"
# COMPRESSION
# Use this to compress the initramfs image. By default, gzip compression
# is used. Use 'cat' to create an uncompressed image.
#COMPRESSION="gzip"
#COMPRESSION="bzip2"
#COMPRESSION="lzma"
#COMPRESSION="xz"
#COMPRESSION="lzop"
# COMPRESSION_OPTIONS
# Additional options for the compressor
#COMPRESSION_OPTIONS=""

which returned all the packages which installed files I was apparently missing. Among them were pambase, shadow several others. After reinstalling them one-by-one manually with pacman my system is back to it's previous state.

Thank you again cfr as well as the rather helpful but rather rude gentleman from IRC